Packet switched handover in a mobile communication system, during which a mobile node receives packets from a source node and a target node

[0001] The invention relates to mobile telecommunications systems. In particular, the invention relates to performing packet switching with a mobile telecommunications system.

Description of the state of the art:

[0002] The introduction of conversation and streaming services in the Global System of Mobile Communications (GSM) has created a demand for efficient switching from the user's point of view in a GSM radio access network (GERAN, GSM / Edge Radio Access Network). The packet data transmission service (GPRS) and the IP multimedia system (IMS, IP Multimedia System) support streaming and conversation services from their side and impose requirements on the GERAN side. This is necessary to be able to perform packet switching (PS) often enough and to be able to minimize interruptions in the continuous packet stream to the mobile terminal. These gaps should preferably be short enough to allow the packet buffering mechanism in the mobile terminal to hide the gaps. Earlier in GPRS, it was sufficient to provide a loss-free connection layer service for interactive applications such as browsing (WAP, Wireless Application Protocol). In browsing applications, moderate additional delays caused by switching are acceptable. However, in streaming and conversational services, gaps in the supposedly continuous packet stream are immediately noticeable, they can, of course, be hidden by using large enough buffers at the ends of call connections. However, always such buffering introduces a delay in the multimedia streams provided to the user. For voice conversation services, significant delays are unacceptable, especially considering other factors that introduce delay in the audio path, such as noise filtering and speech coding.

[0003] Reference will now be made to figure 1, which is a block diagram illustrating the architecture and protocol stacks in the GPRS system in combination with GERAN. The GPRS system is described, for example, in 3GPP 23.060. Stacks of protocols are presented from the point of view of the user plane. In Fig. 1 there is a Gateway GPRS Support Node (GGSN) 106. GGSN 106 is connected to an external network (not shown) via a Gi interface. The external network can be any IP network, for example the internet or intranet. Fig. 1 also has a GPRS service node (SGSN, Serving GPRS Support Node) 104. GGSN 106 communicates with SGSN 104, which establishes packet routes to and from mobile station (MS) 100 via the base station subsystem (BSS, Base Station Subsystem). SGSN 104 takes care of mobility-related tasks, such as having information about the location of mobile station 100, network registrations, updating location and redirection area, activation and deactivation of packet data content (PDP, Packet Data Context), switching and paging of mobile station 100. Of course, some of the above is done by other elements of the network with which SGSN 104 communicates. GGSN is responsible for routing and tunneling packets to and from many SGSN 104 and other SGSN nodes. Routing is based on information about the SGSN address contained in the content of the PDP information contained in GGSN 106 for each network address activated for MS 100, for example on the IP address or X.25 address or PPP link. [0004] In Figure 1, the uppermost protocol layer in MS 100 is the application layer (APPL). The application layer can be any protocol, such as WAP or Transmission Control Protocol (TCP) or Universal Datagram Protocol (UDP). For example, http (Hypertext Transfer Protocol) can be sent via TCP / IP. The communication of the application layer takes place with an equivalent host, which can be located outside the Gi interface, for example in the Internet. Below the application layer is the IP layer, or alternatively the X.25 layer, which in GPRS is supported by both MS 100 and GGSN 106. The IP address for packets intended for MS 100 indicates GGSN 106. The packet IP 114 is transferred to MS 100 from using GPRS user layer protocols below the IP layer. The IP 114 packet is transferred between GGSN 106 and SGSN 104 using the GPRS tunneling protocol (GTP, GPRS Tunneling Protocol). The GTP packet is carried forward via UDP / IP.

[0005] In the SGSN IP 114 packet, data is routed based on the location information of MS 100 and forwarded to the Sub-Network Dependent Convergence Protocol (SNDCP) layer. SNDCP is specified in 3GPP specification 44.065. The SNDCP layer maps the characteristics of the network layer to the characteristics of the basic network. For example, SNDCP deals with the transmission and reception of network layer protocol (N-PDU) data units carrying IP packets. For example, the IP packet 114 is carried in the N-PDU 112. SNDCP multiplexes several packet data packet protocol packets for the same MS. Segments the IP 114 packet into LLC frames, for example the LLC 110 frame. It also merges packets from LLC frames. Header compression and packet usable area compression is also performed at the SNDCP layer. SNDCP negotiates parameters between MS 100 and SGSN 104. SNDCP caches N-PDU for services with confirmed mode.

[0006] Logical Link Control (LLC) provides a reliable connection between MS 100 and SGSN 104. LLC is specified in 3GPP specifications 44.064 and 04.64. The LLC layer is independent of lower radio protocols and hides BSS and radio interface tasks from LCC layer users. LLC supports variable length information frames. LLC supports both confirmed and unconfirmed data transfer, i.e. confirmed and unconfirmed modes of operation. LLC offers services typical of the connection layer including parameter negotiation, flow control in asynchronous balanced mode (ABM Asynchronous Balanced Mode), sequence control to maintain queuing of LLC frames, accelerated delivery for high priority data, error detection, error removal and indication. LLC encrypts data by encrypting the contents of the LLC frame. LLC also supports user identity confidentiality by using a Temporary Logical Link Identity (TLLI) instead of an International Mobile Subscriber Identity (IMSI).

[0007] The relay layer forwards the LLC PDU between UM and GB interfaces in BSS. The Base Station System GPRS Protocol (BSSGP) layer in the 3GPP 08.18 specification carries routing and QoS information between BSS and SGSN. For example, it transfers radio resource requests from SGSN to BSS 102. It also transfers LLC frames between BSS and SGSN. In addition to LLC frames, it also carries PDU signaling units related to GRPS mobility management. The Network Service layer (NS) transports BSSGP PDUs between BSS and SGSN. NS can be based on frame relay (FR, Frame Relay). The RLC sub-layer in the RLC / MAC layer provides a reliable radio technology-dependent connection between MS 100 and BSS 102. The MAC sub-layer performs radio resource requests and reservations, and maps LLC frames to physical GSM channels. The task of the MAC layer is to ensure the effective sharing of a common radio resource by many mobile stations. The RLC / MAC layer is specified in the 3GPP GSM 04.60 specification.

[0008] The standardization organization of 3G cooperation projects (3GPP, 3G Partnership Project) is currently defining the switching with packet switching for the GERAN / GB mode. One of the most important aspects in switching with packet switching is the duplicate forwarding of packets to both the source BSS and destination BSS during the switch, which has not yet been fully included in the specification.

[0009] Reference will now be made to Figure 2, which is a block diagram of GPRS architecture illustrating the problems of the current state of the art associated with the forwarding of duplicate packets. According to the GPRS specification in force, the LLC unit in the new SGSN can only be started up so that the LLC connection is established at the request of the SNDCP unit or equivalent LLC unit. An LLC unit can only be created in its initial state, in which the variable LLC connections have their initial values. In Figure 2 in BSS 216 there are MS 100, base relay stations (BTS, Base Transceiver Stations) 224-228 and base control stations (BSC, Base Controller Stations) 210-214. There is a GGSN 200 node that is connected to the IP 201 network. A 246 downlink packet stream is received from the IP 201 network for which real-time support is required. Initially, the downlink packet stream 246 is tunneled to SGSN 202 as packet stream 240. Initially, SGSN 202 routes packet stream 240 to MS 100 via BSC 212 and BTS 222 as packet stream 242 using an LLC terminating link in LLC 230; which is in MS 100. BSC 212 and BTS 222 are referred to as the source BSS 262. MS 100 communicates with BSC 212 via BTS 222. BSC 212 performs switching tasks including algorithms and decisions to determine the switching. BSC communicates within BSS for signaling associated with SGSN forwarding. Similarly, for signaling associated with MS switching, it communicates with BSC within BSS. Signaling between MS and BSC is via BTS.

[0010] However, when the MS 100 receives a report indicating that a cell supported by BTS 224 has better radio quality, it must begin switching to a cell supported by BTS 224. The new cell is in the area of ​​the new SGSN 204. After switching, the packet stream 246 should be addressed to MS 100 with GGSN 200 via SGSN 204, BSC 214 and BTS 224. BSC 214 and BTS 224 are also referred to as BSS 264 target. While the switchover is not fully completed, SGSN 202 must forward packets to both BSC 212 and SGSN 204. To be able to process packets from packet stream 240, SGSN 204 must receive them as a tunneled 241 GTP packet stream from SGSN 202. Packets from tunneled The 241 GTP packet stream is forwarded in SGSN 204 to its LCC 254. The LLC unit is started from the initial state with the initial LLC connection variables. The tunneled 241 GTP packet stream is routed from SGSN 204 as packet stream 244 carried over an LLC connection. The problem with the duplicate packet forwarding mechanism described above is that the LLC 254 in the new SGSN, namely SGSN 204, has a different state compared to the LLC 252 and 230. This means that the LLC 230 in MS 100 receives packets from two different independent LLCs. The corresponding peer LCC 230 unit in MS 100 is not able to receive packets simultaneously from two different LLC units if the states of LLC units containing LLC variables are not synchronized. Different states generally lead to rejecting LLC frames carrying packet stream 244 or receiving duplicate LLC frames in an uncontrolled manner.

[0011] This rejection is caused by the fact that the LCC 252 sends the LLC frames with consecutive numbers that coincide with the consecutive numbers transmitted by the LCC 254, even if they are different LLC frames. Frames are discarded at unit 230 also due to the fact that LCC 254 sends LLC frames using different encryption parameters. Because the encryption parameters are different, LLC 230 cannot decode LLC frames and rejects them due to failure of Frame Check Sequence (FCS) verification. Another problem is that SGSN 204 is not aware of the sizes of LLC frames negotiated between MS 100 and SGSN 202. If SGSN 204 uses values ​​that exceed the maximum values ​​supported by MS 100, it discards all LLC frames. This in turn can lead to the release of PDP content carrying packet streams 240, 241, 242 and 244. The MS 100 can also perform a reset.

[0012] As explained in 3GPP specification 44.064, the encryption parameters for LLC frames include IOV, LFN, OC and SX. IOV is the Input Offset Value, which is a 32-bit value randomly generated by SGSN. LFN is the LLC frame number (LFN, LCC Frame Number) in the LLC frame header. OC is an Overflow Counter that counts and maintains the status independently on the sending and receiving sides. The OC counter for confirm operation must be set to 0 when the asynchronous balanced operation is re-established for the appropriate Data Link Connection Identifier (DLCI). The LLC layer connection is recognized by DLCI, which consists of the Service Access Point Identifier (SAPI) and TLLI associated with MS 100. The OC counter should be incremented by 512 each time the corresponding LFN overflows. Therefore, OC is never sent directly in LLC frames. The purpose of OC is to add variability in the encryption process to make it more resistant. SX is the XOR mask calculated from the LLC entity identifier. There are two IOV values, one for numbered information frames related to confirmation activities and the other for unconfirmed information frames related to confirmation activities. There are also two LFN values, one for action with confirmations and the other for action without confirmation. There are four OC counters associated with each DLCI. One OC meter falls for each operating mode, which is without confirmation or with confirmation and there is a transmission direction, which is uplink or downlink.

[0013] Of course, the session key Kc used in the encryption algorithm is one of the encryption parameters.

[0014] Reference will now be made to figure 3, which is a signaling diagram illustrating signaling during handover with packet switching, in accordance with current 3GPP proposals. Current proposals are described in document TSG GP-032710 "Switching with packet switching for GERAN A / GB mode, stage 2" version 0.2.0, 2004-01. The signaling architecture is as shown in figure 2. Using message 301, MS 100 sends radio quality measurement information regarding the measurement of cells adjacent to the source BSS 262. Based on the measurement information, the source BSS 262 determines that a switch is needed. At t0, the source BSS 262 determines that a switch is to be made to a new cell that is in the area of ​​the new SGSN, which is SGSN 204. The source BSS 262 sends a message 302 to the old SGSN 202 that a PS switch is required. The message includes, for example, the source cell, target cell, TLLI, and cause, and the transparent SGSN 202 determines based on the target cell whether the switch is a switch within or between SGSN. SGSN 202 determines the identification of the new SGSN and sends a message 303 requesting PSPS switching preparation to SGSN 204. SGSN 204 sends a message 304 that a PS transfer is required that requests the target BSS 264 to reserve radio resources for MS 100 in the target cell. When radio resources have been allocated successfully, target BSS 264 sends a PS switch request confirmation message 305 indicating successful allocation. SGSN 204 sends a message 306 response to switch preparation to SGSN 202, which informs, among other things, that SGSN 202 can send a command to MS 100 to complete the switch to a new cell. SGSN 202 receives message 306 at t1.

[0015] At the same time, however, the packet from the GTP packet stream 307 is received by SGSN 202. SGSN 202 sends packets one by one from the GTP packet stream 307 to SGSN 204 as packet stream 308. SGSN 204 sends packets from packet stream 308 further to destination BSS 264 as packet stream 309. Destination BSS forwards packets from packet stream 308 to MS 100 as packet stream 310. There is a delay before MS 100 is able to receive packets from SGSN 204 via target BSS 264. SGSN 202 sends a 311 PS switch command message to the source BSS 262. The source BSS then sends a PS switch command message to the MS 100. Then, the MS 100 tunes to the radio channel and the time slot allocated to the target cell by the target BSS 264. This is indicated by arrow 312. Target BSS 264 sends physical information to MS 100 so that the MS 100 synchronizes. After synchronization, the MS 100 sends a message 314 about the completion of the PS switchover to the target BSS 264 during t2. Only after time t2 MS 100 is prepared to simply receive packets via target BSS 264, which means that there is an unacceptable delay unless MS 100 receives packets through both target BSS 264 and source BSS 262. Destination BSS 264 sends a message 315 about the completion of the PS switch to SGSN 204. Then, SGSN 204 updates the PDP content, as shown by arrows, 316 and 317 at GGSN 200. The update of the PDP content indicates GGSN 200 the address of the current SGSN 204. After receiving the update PDP content at t3, GGSN 200 is able to start routing the 318 GTP packet stream to the correct SGSN, which is now SGSN 204. Then, MS 100 receives packet stream 320 from destination BSS 264, which was received from SGSN 204 as packet stream 319.

[0016] Reference will now be made to figure 4, which is a signaling diagram illustrating the delay associated with a solution that merely forwards packets from the source node to the destination node during the handover. This solution is similar to the solution used in the UMTS system in connection with moving the server operating the SRNS radio network (Serving Radio Network Server). SRNS porting is explained in 3GPP 23.060. In Figure 4, the source node 452 receives the packet stream 401 sent by the parent node 450, which is connected to the IP network 451. At time t0, the parent node sends the specific packet 460 in the packet stream 401. The source node also redirects the packet stream 402 to MS 100 via access network 456. At t1, MS 100 decides to start using destination node 454 instead of source node 452 to receive packet streams. At time t1, MS 100 confirms the last frame received from the source node 452 using message 403. The packet 460 has not been received in full, for example the last frame from packet 460 may have just been received. MS 100 sends a request message 403 to the source node 452 indicating the cancellation of the source node 452 for MS 100 traffic. After receiving message 403, source node 452 begins forwarding all packets destined for MS 100 via destination node 454 as packet stream 405. Packet stream 405 is forwarded by destination node 454 to MS 100 as packet stream 406. At t2, MS 100 receives the first packet since MS 100 received the last frame via source node 452 at t1. The time difference between t1 and t2 means a pause in receiving packets in MS 100, and the time difference between t0 and t2 means a delay in receiving packet 460 from the parent node 450 to MS 100. The delays explained above are not acceptable for real time services.

[0017] As has been shown with reference to figures 2, 3 and 4, there are problems with implementing switching with packet switching using the current GPRS architecture and the solutions proposed in the current state of the art. On the one hand, it must be possible for MS to simultaneously receive packets from the source node and the destination node when signaling switchover. On the other hand, this is not possible in current GPRS specifications and leads to rejection of forwarded frames on the MS side.

[0018] The corresponding publication WO 01/35586 discloses a method and apparatus for facilitating network-controlled switching in a wireless network that utilize packet switching and uses common resources such as time slots and provide a network unit controlled mobile unit switching through a station system base by providing packet routing to multiple mobile units to facilitate switching of at least one mobile unit. The base station system uses memory containing stored data of the required radio resources, for example, information about the content of PDP, converted into mobile units. With the ability to route packets, store and service the required data for shared radio resources permanently at the base station system level in the network, it is possible to perform a network controlled switchover without supervision of the network element with packet switching that provides packages for the base station system. There is a base station system that includes a packet switching controller that communicates with a shared radio resource controller adapted to provide packet routing of received data packets for many mobile devices. The memory is connected to the packet switching controller, and contains stored data of the required radio resources that contain information about the contents of the PDP. The packet switching controller is adapted to determine the appropriate target cell for at least one mobile unit based on stored data of required radio resources and contained information about the content of PDP.

[0019] The relevant publication US 6,137,783 discloses a system and method for reducing or eliminating the transfer of mobility management information of a mobile terminal caused by temporary signal interference blocking communication. When the distance of the mobile terminal from the base station serving the first network system exceeds the threshold, the distances between the mobile terminal and other base stations (serving other network systems) are determined, and the shortest distance corresponding to the second network system is selected, and the control transferred. However, the mobility management information for the mobile terminal present in the first network system remains in the first network system after the transfer of control, the information being available to the second network system via a packet switch connecting the first and second network systems together.

[0020] The corresponding publication US 2003/091011 discloses a telecommunications network that is able to efficiently and efficiently support the mobility of wireless user terminals between access point nodes in a packet switching network with minimal redundancy and packet loss. The telecommunications network uses a backbone network with packet switching and numerous access points connected to the backbone network. Each access point is adapted to provide any user terminal with wireless access to the core network when that user terminal is connected to that access point. The system and method further uses ad-hoc routing techniques when switching the user's wireless terminal between access point nodes in the backbone network to allow the network to maintain multiple data transmission paths by which packets are delivered to the user terminal during switching to substantially eliminate losses packets when switching. US 2003/091011 relates to IP layer mobility based on address caching.

[0021] The corresponding publication US 2002/066011 discloses a method in which, when setting up a connection to a first radio access network, a multi-mode mobile station sends an initial unsecured initial signaling message that contains information about those encryption algorithms that the multi-mode mobile station supports when connects to the other radio access network. The first radio access network stores some or all of the information. Then, it creates and sends a protected integrity message that contains information about the encryption algorithms supported by the multimode mobile station in the second radio access network.

[0022] The corresponding publication US 2002/115460 discloses a method in which, in a radio access network of a mobile telecommunications system, the radio network controller determines the nominal power level to be used by the base station when transmitting a common connection channel via a radio interface in a cell for a connection comprising a unit of equipment user. The nominal power level is set by the radio network controller, regardless of whether the base station supports a differential power control scheme. The differential power control scheme allows the base station to selectively adjust the nominal power level, according to whether the cell served by the base station is the primary cell or not the primary cell for connection to the user equipment unit. When the cell is a primary cell, the base station adjusts the nominal power level by subtracting the correction value from the nominal power level to determine the power level used for current data transmission on the common connection channel via the radio interface. In different embodiments, the correction value is obtained either from the radio network controller or it is locally configured for the base station.

[0023] The corresponding publication EP 0 978 958 discloses a method for determining a control channel in a mobile telecommunications system in which a mobile station treats multiple telephone calls using a plurality of sets of wireless communication resources, where a single control channel is established between the mobile station and the network for carrying control information between them in such a way that the control channel is formed by one of sets of wireless communication resources, which are used by the mobile station for many connections.

Summary of the invention:

[0024] The invention relates to a method of performing packet switching with a mobile telecommunications network, comprising a mobile node, a first and a second packet switching node, the method comprising: detecting the switching state associated with said mobile node in said first packet switching node, a request preparing a switch by said first packet switching node from said second packet switching node. This method is characterized in that it further comprises: receiving at least one scrambling parameter from said first packet switching node to said second packet switching node when said first packet switching node requests preparation of a switch from said second packet switching node, receiving logical connection layer state information from said first packet switching node to said a second node switching packets, setting the state in the logical connection layer unit at said second node switching packets based on said state of the logical connection layer, and sending logical connection layer frames from said layers of the first and second node switching packets to said mobile node during handover.

[0025] The invention also relates to a method of performing packet-switched switching in a mobile telecommunications network, comprising a mobile node, a first and a second packet switching node, the method comprising: detecting the switching state associated with said mobile node in said first packet switching node, a request to prepare carrying by said first packet switching node from said second packet switching node. The method is characterized in that it further comprises: receiving at least one scrambling parameter from said first packet switching node to said second packet switching node when said first packet switching node requests preparation of a switch from said second packet switching node; receiving a packet at said first packet switching node; creating a protocol data unit (PDU) of the logical connection layer from the data in said packet; sending a first frame including said protocol data unit (PDU) of the logical connection layer to said mobile node from said first packet switching node; sending said protocol data unit (PDU) for logical connection from said first packet switching node to said second packet switching node, and sending a second frame containing said protocol data unit (PDU) of logical connection layer to said mobile node from said second packet switching node.

[0026] The invention also relates to a method of performing packet switched switching in a mobile telecommunications network, comprising a mobile node, a first and a second packet switching node, the method comprising: detecting the switching state associated with said mobile node at the first packet switching node and a request to prepare a switch , by said first packet switching node from the second packet switching node. The method is characterized in that the method further comprises: receiving at least one scrambling parameter from said first packet switching node to said second packet switching node when said first packet switching node requests the preparation of a switch from said second packet switching node; performing an exchange of logical connection parameters between said mobile node and the first packet switching node, and sending logical connection layer frames from said first and second packet switching node to said mobile node during handover.

[0027] The present invention also relates to a method of performing packet-switched switching in a mobile telecommunications network, comprising a mobile node, a first and a second packet switching node, the method comprising: creating a first logical connection layer unit at said mobile node and detecting the switching state of said node moving. The method is characterized in that the method further comprises: receiving at least one scrambling parameter from said first packet switching node to said second packet switching node, when said first packet switching node requests preparation of a switch from said second packet switching node, creating a second logical connection layer unit at said mobile node, sending logic connection layer frames from said first and second packet switching nodes to said mobile node during handover; detecting completion of the switch, and re-negotiating the parameters of the logical connection layer between said mobile node and said second packet switching node after said detection of said switch end when the parameters of the logical connection layer are not adequate.

[0028] The invention also relates to a system in which packet switching is performed between the first packet switching node and the second packet switching node. The system is characterized by the fact that the system includes: a mobile node that is adapted to receive a logical connection layer frame from said first and second packet switching nodes during handover, the first packet switching node is adapted to detect the handover state associated with said mobile node to request switch preparation from said second packet handover node . for sending at least one encryption parameter to said second packet switching node, during a request to prepare transfer from the second packet switching node, to send information about the state of the logical connection layer to said second packet switching node, and the second packet switching node is adapted, to set the state in a logical connection layer unit based on the state of said logical connection layer.

[0029] The invention also relates to a system in which packet switching is performed between the first packet switching node and the second packet switching node. The system is characterized in that the system comprises: a mobile node adapted to receive a logical connection layer (PDU) data unit from said first packet switching node and a second packet switching node; the first packet switching node is adapted to detect the switching state associated with said mobile node, requesting the preparation of a switch from said second packet switching node, to send at least one encryption parameter to said second packet switching node, during the request to prepare a switch from said second node packet switching; for receiving a packet from a logical data layer (PDU) logical connection layer data from said packet data for sending a first frame containing said logical data layer (PDU) logical data layer unit to said mobile node, for sending said logical data protocol unit (PDU) to said second packet switching node; and a second packet switching node, adapted to send a second frame including said protocol data unit (PDU) of the logical connection layer to said mobile node from said second packet switching node.

The invention also relates to a system in which packet switching is performed between the first packet switching node and the second packet switching node. The system is characterized by the fact that the system includes: a mobile node adapted to receive a logical connection layer frame from said first and second packet switching nodes during handover, the first packet switching node is adapted to detect the handover state associated with said mobile node to request switch preparation from said second packet switching node, for sending at least one ciphering parameter to said second packet switching node when the node requests preparation of a switch from said second packet switching node, to perform an exchange of logical connection parameters between said mobile node and said first packet switching node, and to send the logical connection layer frame to said mobile node during switching, and a second packet switching node, adapted to send the logical connection layer frame to said mobile node during handover.

[0031] The invention also relates to a system in which packet switching is performed between the first packet switching node and the second packet switching node. The characteristic system is that it includes: a mobile node adapted to create the first logical connection layer unit, to detect the switch state, to create the second logical connection layer unit, to detect the completed switch state, to receive the logical connection layer frames from the first packet switching node, and the second node switching packets during switching, with the first node switching packets, is adapted to send at least one encryption parameter to said second packet switching node when requesting a switch preparation from said second packet switching node and to send logical connection layer frames to said mobile node during switching, the second packet switching node is adapted to re-negotiate the parameters of the logical connection layer between said mobile node and the second packet switching node after said detection of said switching state when the parameters of the logical connection layer are not suitable.

[0032] In one embodiment of the invention, the mobile node is a mobile terminal, e.g. a UMTS terminal, GSM terminal, GPRS terminal, WLAN terminal or terminal within any cellular telecommunications system.

[0033] In one embodiment, the mobile node is a portable computer, for example, a laptop computer, palmtop or Personal Digital Assistant (PDA).

[0034] In one embodiment of the invention, the mobile telecommunications system relies on packet data (GPRS), the first and second node switching packets are nodes supporting GPRS services (SGSN), and the logical connection layer is controlling GPRS logical connection ( LLC) and the exchange of the logical connection parameter is to negotiate the exchange of the logical connection control (LLC) (XID). In one embodiment of the invention, the second packet switching node is a base station subsystem (BSS) node, e.g., base station controller or base station. In one embodiment of the invention, the first or second packet switching node is a node that performs the forwarding and switching of data packets at the connection layer. The invention is not limited to packet switching nodes that switch packets at the network layer level, such as e.g. IP routers. Packets in this document are understood as data packets referring to each protocol layer, e.g., network layer packets, connection layer frames, asynchronous transfer mode (ATM) cells.

[0035] In one embodiment of the invention, the exchange of the logical connection parameter is performed in response to detecting the switching state at the first packet switching node.

[0036] In one embodiment of the invention, the first logical connection layer unit at the mobile node is removed upon detection of the switch completion.

[0037] In one embodiment of the invention, the at least one encryption parameter is received from the first packet switching node to the second packet switching node when the first packet switching node requests the preparation of the switch from the second packet switching node. This means that at least one encryption parameter is transmitted from the first packet switching to the second packet switching in the message that requests the preparation of the switch.

[0038] In one embodiment of the invention, the logical connection layer information is received from the first packet switching node to the second packet switching node when the first packet switching node requests switch preparation from the second packet switching node. This means that the logical connection layer information is sent from the first packet switching node to the second packet switching node in the message requesting switch preparation.

[0039] In one embodiment of the invention, the exchange of the logical connection parameter is performed in response to a state when the mobile node receives an LLC frame that has a duplicate flag set. The duplicate marker indicates the duplication of the frame

LLC for switching purposes. In one embodiment of the invention, the duplication tag is accepted by the mobile node only when performing the switch. Otherwise, receiving the tag results in an error indication for the peer LLC.

[0040] In one embodiment of the invention, the logical connection layer means at the mobile node, at the first and second packet switching nodes are represented by one or more logical connection control units (LLC), logical link management units (LLME, Logical Link Management Entity) and a multiplexing unit associated therewith. During transmission, the multiplexing unit generates and inserts FCS, performs the frame encryption function and ensures that the content of the logical connection control layer is distinguished based on SAPI between different logical connection units. The functions implemented by the multiplexing unit and LLME are described in 3GPP 23.060.

[0041] In one embodiment of the invention, the control means in the first and second packet switching nodes comprise higher protocol layer units above the logical connection layer. For example, in SGSN, control means may include relay layer units, SNDCP layer units, and GTP layer units.

[0042] In one embodiment of the invention, the control means at the mobile node include higher protocol layer units relating to the user's GPRS plane.

[0043] In one embodiment of the invention, the signaling means at the mobile node include signaling protocols for communicating with the first and second packet switching nodes. In the GPRS mobile terminal, the signaling means include units of the stack of GPRS control plane signaling protocol. In one embodiment of the invention, the actual mobility management and logic of the radio control application are implemented in the control means or in separate control means in connection with the signaling means. In one embodiment, the exchange of signaling messages is supported by separate means for this task.

[0044] In one embodiment of the invention, the signaling means at the first and second packet switching nodes include signaling protocols used for communication with the mobile node. In SGSN, the signaling means include GPRS control plane control protocol stack units.

[0045] In one embodiment of the invention, the sending of logical connection layer frames or any other messages between the mobile node and the packet switching nodes is implemented by means of a radio access network, such that the frames and messages are forwarded by one or more elements of the intermediate network, such like base station controllers, radio network controllers and base relay stations. In one embodiment of the invention, the first and second packet switching nodes are directly connected to the base relay stations and directly manage the radio network control procedures.

[0046] The benefits of the invention are associated with improved quality of service. With this invention, it is possible to provide a continuous stream of packets to a mobile station during handover.

Brief Description of the Drawing Figures [0047] The accompanying drawing figures, which are attached for an additional understanding of the invention and which form part of the present description, illustrate embodiments of the invention and together with the description, help explain the principles of the invention. In the drawing:

Fig. 1 is a block diagram illustrating the structure of the state of the art and protocol stacks of the GPRS (General Packet Radio Service) system in connection with a GSM / EDGE radio access network (GERAN);

Fig. 2 is a block diagram illustrating the GPRS (General Packet Radio Service) architecture and problems of the current state of the art related to the forwarding of duplicate packets;

Fig. 3 is a signaling diagram showing signaling of the prior art during handover switching;

Fig. 4 is a signaling diagram illustrating the delays associated with a solution that merely forwards packets from the source node to the destination node during the handover;

Fig. 5 is a signaling diagram illustrating one embodiment of a method for performing packet switching with state transfer according to the invention;

Fig. 6a is a block diagram illustrating one embodiment of a method for performing packet switching, using frame forwarding by a GPRS enabled node (SGSN) according to the invention;

Fig. 6b is a block diagram illustrating one embodiment of a packet switching method using frame forwarding directly to a target base station subsystem according to the invention;

Fig. 7 is a signaling diagram illustrating one embodiment of a packet switching method using a logic connection parameter reset according to the invention;

Fig. 8 is a block diagram illustrating one embodiment of a packet switching method using duplicate logic connection control units according to the invention;

Fig. 9 is a signaling diagram illustrating one embodiment of a packet switching method using a duplicate frame indicator according to the invention;

Fig. 10 is a flowchart illustrating one embodiment of a packet-switched switching method using content transfer according to the invention;

Fig. 11 is a flowchart illustrating one embodiment of a packet switching method using frame forwarding according to the invention;

Fig. 12 is a flowchart illustrating one embodiment of a packet switching method using logical link reset according to the invention;

Fig. 13 is a flowchart illustrating one embodiment of a packet switching method using duplicate logic connection control units according to the invention;

Fig. 14 is a flowchart illustrating one embodiment of a packet switching method using a duplicate frame indicator according to the invention;

Fig. 15 shows a node supporting GPRS (SGSN) in one embodiment of the invention; and

Fig. 16 shows the mobile node in one embodiment of the invention.

Detailed Description of Embodiments [0048] Detailed reference will now be made to an embodiment of the present invention, examples of which are illustrated in the accompanying drawings.

[0049] Figure 10 is a block diagram showing one embodiment of packet switching which uses state transfer using the signaling shown in figure 5. The signaling is performed in the architecture of the GPRS system as illustrated in figure 2. In step 1000, check whether there is a switch. In the event that switching occurs, the MS 100 sends radio-quality measurement information about neighboring cells to the source BSS 262 via message 301. Based on the measurement information, BSS 262 determines that switching is needed. This determination is performed using an algorithm that is performed in the base station controller (BSC) within the source BSS 262. At t0, the source BSS 262 determines that a switch is to be made to a new cell that is within the new SGSN, which is SGSN 204. The source BSS 262 sends a message 302 about the required PS switch to the old SGSN 202. The message includes, for example , source cell, target cell, TLLI, cause and transparent medium. SGSN 202 determines based on the target cell whether the switch is a switch within or between SGSN. SGSN 202 sets the identifier for the new SGSN and sends a message 303 requesting PS switch preparation to SGSN 204.

[0050] In step 1002, the state relating to the logical connection is obtained from LLC 204 in SGSN. This is achieved in that the switch prepare request message carries LLC status information element 500. LLC status information element 500 contains information that is used to synchronize LLC units in SGSN 202 and SGSN 204. The information element 500 contains at least the session key Kc, IOV values ​​for both modes of operation, both IFN values ​​and four OC values. SGSN 204 keeps information element 500 until SGSN 202 forwards packets to it. The signaling of switching between network elements continues as explained in connection with figure 3.

[0051] In step 1004, when the first forwarded packet is received from the SGSN 202, the LLC unit is initialized in SGSN 204. During initialization, SGSN 204 uses the information element 500. By having the information element 500 and the LLC status information contained therein, it is possible is for SGSN 204 the creation of an LLC unit, which is an exact copy of the LLC unit in SGSN 202 from the point of view of MS 100. Then, the MS 100 is able to receive LLC frames from both LLC units without noticing the difference. In one embodiment of the invention, the LLC unit in SGSN 204 is initialized and started after SGSN 204 has received message 303, and no packets to be forwarded have yet been received by SGSN 204. In step 1006, SGSN 204 begins forwarding packets received through SGSN 202 using the LLC unit created and initialized in step 1006.

[0052] Figure 11 is a flowchart illustrating one embodiment of packet-switched switching that uses frame forwarding in a system as shown in Figures 6a and 6b. At step 1100, SGSN 202 waits for a message from the source BSS 262 indicating that switching is required. In one embodiment of the invention, the handover indication may also be received from MS 100. When the message is received, the method continues at step 1102. At 1102, SGSN 202 waits for an event in which the SGSN 202 receives a packet 610 from GGSN 200, which is the first user plane packet after switching has started. In this case, the first LLC 614 frame that carries data from packet 610 is to be sent by SGSN 202. When this event occurs, packet 610 is received by the SNDCP unit 600 in SGSN 202 via GTP and relay layers as shown in Figure 1.

[0053] The packet 610 is received at SGSN 202 via tunnel 240. The SNDCP unit 600 performs packet segmentation for packet 610 and other SNDCP layer tasks, and sends a request to LLC 252 to send the first frame LLC 614. The request is sent as a data unit controlling LLC (SDU, Service Data Unit). At step 1104, LLC 252 prepares an LLC-PDU using information contained in the state variables of LLC 252 and LLC-SDU. At step 1106, LLC 252 sends the prepared LLC-PDU in the first frame LLC 614 to the source BSS 262 and BSC 212 in it.

[0054] At 1108, LLC unit 252 passes LLC-PDU in second frame LLC 616 to frame transfer unit 604 associated with SNDCP 600 unit. It should be noted that second frame LLC 616 is a duplicate frame LLC 614. Frame transfer unit 604 sends a second frame LLC 616 to SGSN 204 using connection 241, which tunnels LLC frames prepared by LCC 252 to SGSN 204. The connection 241 is, for example, a GTP tunnel established between SGSN 202 and SGSN 204 for transparent transmission of LLC frames. The second LLC 616 frame is received by unit 606 in SGSN 204. The LLC 606 unit is adapted to receive LLC frames via connection 241 and forward it transparently to destination BSS 264. Transparent transmission means in this case that the LLC unit does not change the frame fields LLC defining the status of LLC 252. In one embodiment of the invention, the LLC PDU relay formed from the LLC 616 frame is not forwarded by the SNDCP protocol unit in SGSN 204. In another embodiment of the invention, the LLC PDU from the LLC 616 frame is forwarded via the chain of the GTP-SNDCP-LLC-BSSGP protocol unit in order for it to be sent to target BSS 264.

[0055] In one embodiment of the invention shown in Figure 6b, SGSN 202 passes the second frame LLC 616 directly to BSS 264. This is achieved so that 241B creates a connection between SGSN 202 and the target BSS 264. This is done so that step 1108 is omitted in the way. Instead, in step 1110 the LLC unit 252 passes LLC-PDU in the second LLC frame 616 to the frame forwarding unit 604b associated with the SNDCP unit 600. The frame forwarding unit 604b sends the second LLC frame 616 to the target BSS 264 using connection 241b. Destination BSS 264 is configured to receive LLC 616 and other duplicate LLC frames to switch and to prepare them for transmission to MS 100. [0056] Figure 12 is a flowchart illustrating one embodiment of packet switching which uses the logic connection reset obtained by the signaling shown in figure 7. The signaling is performed in the GPRS system architecture which is illustrated in figure 2. At step 1200 it is checked if there is a switch. In the event that switching occurs, the MS 100 sends radio-quality measurement information about neighboring cells to the source BSS 262 via message 301. Based on the measurement information, the source BSS 262 determines that switching is needed. This determination is performed using an algorithm that is performed in the base station controller (BSC) within the source BSS 262. At this time, the source BSS 262 determines that a switch is to be made to a new cell that is in the area of ​​the new SGSN, which is SGSN 204. The source BSS 262 sends a message 302 about the required PS switch to SGSN 202. The message includes, for example, source cell, target cell, TLLI, cause and transparent medium. SGSN 202 determines based on the target cell whether the switch is switching within or between SGSN. SGSN 202 determines the identity of the new SGSN, which in this case is SGSN 204, and sends a message 303 requesting the preparation of switching PS to SGSN 204.

[0057] At step 1202, SGSN 204 obtains the encryption parameters related to the logical connection in the SGSN 204. This is achieved in such a way that the PS switch preparation request message carries the information item about the ciphering parameters 700. The information item 700 includes, for example, the session key Kc and any other parameters not negotiated again during the XID reset procedure. At step 1204, SGSN 202 starts the XID reset procedure so that LLC 252 in SGSN 202 sends an XID 701 command message to MS 100 via the source BSS 262. XID command message 701 contains information about LLC parameters, such as, for example, LLC version number, IOV values, retransmission timeout, maximum retransmission number, maximum information field length in two confirmation modes, frame buffer size in downlink and uplink direction, sizes windows towards downlink and uplink and layer-3 parameters. XID command message 701 proposes LLC parameter values ​​that correspond to the initial values ​​set when the new SGSN initializes its LLC unit. After receiving the XID command message 701, MS 100 sets the LLC parameters to the proposed values ​​and sends the XID response message 702 confirming the proposed parameter values. In one embodiment of the invention, MS 100 is adapted to automatically confirm the parameters proposed by SGSN 202 when it is aware that the switching process is in progress. In one embodiment of the invention, the MS 100 automatically accepts a PDU downlink from SGSN 204 if it is tagged appropriately and if it is received during handover.

[0058] At 1206, SGSN 204 starts receiving packets forwarded from SGSN 202. In Figure 7, these packets are carried in packet stream 308. SGSN 204 initializes its LLC unit 254 to have initial LLC parameter values. The initial values ​​correspond to the values ​​of the LLC parameters negotiated between SGSN 202 and MS 100 during the XID reset procedure in step 1204. Then, SGSN 204 starts sending forwarded packets towards MS 100. Then SGSN 204 and MS 100 can negotiate more optimal LLC parameters. Usually, the re-negotiation of LLC parameters is performed after the routing area is updated.

[0059] Figure 13 is a flowchart illustrating one embodiment of a packet switching with the configuration shown in the figure

8. At step 1300, MS 800 has only one LLC unit, which is the first LLC 802 unit. The first LLC 802 unit is equivalent to the LCC 252 unit in SGSN 202. There is an LLC 842 connection between LLC 252 and 802 units. The LLC 842 connection carries the packet stream from GGSN 200 to MS 800. MS 800 is waiting for a state in which switching is required. This is determined based, for example, on a switch command received from BSS 262. When the state is detected, the method continues at step 1302. At step 1302, MS 100 forms a second LLC 804 that exists simultaneously with the first LLC 802 at least during the switch. The second LLC 804 is equivalent to LCC 254 in SGSN 204. In step 1304, MS 800 initializes the second LLC 804. The LLC parameters are initialized to values ​​consistent with the values ​​to which SGSN 204 initializes the LLC parameters when initializing the LLC 254 in step 1306. In step 1306, SGSN 204 receives packets forwarded from SGSN 202 via tunnel connection 241. Tunnel connection 241 is, for example GTP tunnel. SGSN 204 sends forwarded packets towards MS 800 using the LLC 844 connection that it establishes between LLC units 254 and 804. At step 1308, MS 800 checks to see if the switchover is complete. If the handover has not been completed, the method continues at step 1308.

[0060] After the switch is completed, the LLC 842 connection between LLC units 252 and 802 is no longer used to carry LLC frames. In one embodiment of the invention, in step 1310, MS 800 checks whether the parameters relating to the LLC 844 connection are suitable to take into account, for example, the radio conditions in a cell supported by BTS 224. MS 800 can also adjust the parameters depending on the available memory and data rate on the LCC 844 connection. In one embodiment of the invention, the parameters of the LLC 254 unit are first initialized to average values ​​that have been created to be suitable for most mobile stations under various radio conditions. Mobile stations can also have different memory sizes and software versions. Sizes, e.g., information field lengths, frame and window buffer sizes, can first be set to lower values ​​than would otherwise be negotiated between equivalent LLC units. If MS 800 determines that pa16 ramethers LLC are not suitable, it tunes them to other values ​​in step 1312. The parameters are to be re-adjusted, for example, using the XID reset procedure involving the exchange of XID commands and XID responses between LLC 804 and 254. If the parameter values ​​are correct, you do not need to re-adjust them.

[0061] In one embodiment of the invention after the switch is completed, MS 800 removes the first LLC unit that was used before the switch. At step 1314, MS 800 performs the necessary procedures to remove an LLC 802 entity that is no longer used. MS 800 can also remove LLC 802 immediately after step 1308 before checking if the LLC parameters are appropriate. Deleting the LLC unit includes, for example, releasing memory reserved for use by the LLC 802 unit and the LCC 842 connection in MS 800. Similarly, information regarding the LLC 802 unit and the LCC 842 connection may be removed from tables stored in MS 800.

[0062] Figure 14 is a flowchart showing one embodiment of a packet switching method that uses the duplicate frame indicator carried and processed using the signaling shown in figure 9. The signaling is performed in the GPRS system architecture, as illustrated in figure 2. step 1400 checks if there is a switch. When switching occurs, the MS 100 sends radio-quality measurement information about the cells neighboring the source BSS 262 via message 301. Based on the measurement information, the source BSS 262 determines that switching is required. This determination is performed using an algorithm that is performed in the base station controller (BSC) within the source BSS 262. At t0, the source BSS 262 determines that a switch is to be made to a new cell that is in the area of ​​the new SGSN, which is SGSN 204. The source BSS 262 sends a message 302 about the required PS switch to SGSN 202. The message contains, for example, source cell, target cell, TLLI, cause and transparent medium. SGSN 202 determines, based on the target cell, whether the switch is internal or non-SGSN. SGSN 202 determines the identification of the new SGSN, which in this case is SGSN 204 and sends a message 303 requesting the preparation of switching PS to SGSN 204.

[0063] At step 1402, the encryption parameters regarding the logical connection are obtained by the LLC entity in SGSN 204. This is obtained in that the PS switch preparation request message carries the element 700 of information about the encryption parameters. The information element 700 contains, for example, the session key Kc and any other parameters not negotiated again during the XID reset procedure.

[0064] In step 1404, SGSN 204 waits for packets forwarded to it from SGSN 202. When such a packet is received in message 308, the method continues in step 1406. In step 1406, the SNDCP unit in SGSN 204 points to the LLC unit in SGSN 204 during request to send LLC-SDU so that LLC-SDU is the first LLC-SDU containing data from packets transferred from SGSN 202 to SGSN 204. The LLC-PDU is therefore a duplication of another LLC-PDU sent from SGSN 202. The LLC unit in SGSN 204 sets a duplicate for the switch marker in the LLC-PDU header to be sent. The flag may be carried, for example, in one of the reserved bits in the LCC address field or in one of the bits of the UI control field. Therefore, no additional bits are needed in the LLC-PDU header. The LLC parameters are set to the default switching values. Default values ​​can be normalized so that optimization is maximized or normal default values ​​are used. When the MS 100 receives an LLC-PDU in the LLC frame, it detects that the copy for the switch bit is set. At step 1408, the MS performs an implicit XID reset on the LLC unit it contains. In implicit reset, the XID MS 100 automatically sets the LLC parameters to values ​​that match the values ​​set by the unit

LLC in SGSN 204, when it is created and initialized for the first time. An implicit XID reset is required in MS 100 before it can process any LLC frames from SGSN 204. For example, this is due to various encryption parameters, such as an overflow counter, which were not received at step 1402.

[0065] Figure 15 shows a GPRS enabled node (SGSN) in one embodiment of the invention. SGSN 1500 includes a signaling unit 1504 that communicates with the logic link layer unit 1506. Signaling unit 1504 performs signaling of the GPRS control plane. The logical connection layer entity 1506 carries both the control plane and the user plane messages as defined in 3GPP 23.060 regarding LLC. In the embodiment of the invention illustrated in connection with the description of Figures 6 and 11, the logical connection layer 1506 unit is responsible for creating the logical connection layer data (PDU) units and sending the logical connection layer data (PDU) units to the new SGSN. In one embodiment of the invention, the sending of the logical connection PDU layer data units to the new SGSN is obtained so that the logical connection layer unit 1506 forwards the PDUs to the control unit 1502, which sends them via, for example, the GTP 1510 unit to the new SGSN. In one embodiment of the invention, the signaling unit 1504 is responsible for detecting the switch state, requesting the switch preparation from other SGSN nodes, receiving switch preparation requests from other SGSN nodes, sending information about the state of the logical connection layer, encryption parameters, and other information for other SGSN nodes . In one embodiment of the invention, ongoing mobility management and application procedures related to signaling messages received by signaling unit 1504 are performed by control unit 1502 or by a separate control unit within signaling unit 1504. In one embodiment of the invention, the control unit 1502 is responsible, for example, for setting the state in the logical connection layer unit 1506 based on the logical connection layer information received from another SGSN and for sending the logic connection layer frames to the mobile node during handover. The actual transfer of logical link layer frames is via the lower 1508 protocol layers. The arrows in Figure 15 show the directions of information flow between units within SGSN 1500.

[0066] Figure 16 shows the mobile node in one embodiment of the invention. In figure 16, the mobile node is in particular a GPRS mobile terminal. Mobile node 1600 includes a signaling unit 1604 that communicates with a logic link layer unit 1606. The logical connection layer unit 1606 carries both the control plane and the user message plane as defined in 3GPP 23,060. In one embodiment of the invention, the signaling unit 1604 is responsible for receiving signaling messages from the base station subsystem and detecting switch states and completion of the switch based on the received signaling messages. The logical connection layer 1606 unit performs tasks associated with the logical connection control protocol (LLC). In the embodiment of the invention shown in connection with the description of Figure 12, the logical connection layer unit 1606 is adapted to negotiate the parameters of the logical connection layer with the new SGSN after the switch is completed. Mobile station 1600 also includes a control unit 1602 that performs tasks associated with higher layer protocols and overall communication coordination. In one embodiment of the invention, the control unit 1602 is adapted to form the first logical connection layer unit during the connection establishment procedure and the second logical connection layer unit in response to the switching state. The arrows in Figure 16 illustrate the directions of information flow between units within a mobile node

1600.

[0067] It is obvious to a person skilled in the art that, as technology advances, the basic idea of ​​the invention can be implemented in various ways. The invention and its embodiments are therefore not limited to the embodiments described above, as they may vary within the scope of the claims